AGL_Unit_LOCU_EN_Rev00
21
The regulation starts when the suction pressure (
AI1
) increases and reaches the value
(C16-C17/2+(C17*C24)/100). Within the adjustment range (C16-C17/2 ~ C16+C17/2) the digital
scroll compressor is activated in PWM mode according to the value of the control variable.
When the pressure is higher than (C16+C17/2) then the TRIAC output is at maximum capacity. When
the pressure is lower than (C16+C17/2) but higher than (C16-C17/2) the digital compressor
modulates the capacity according to the proportional band. If the pressure is lower than (C16-C17/2)
the digital compressor switches off.
NOTE: When the digital valve on the compressor is discharged the compressor is loaded.
NOTE: At start-up the valve is energized for C20 start-up time, ie, time interval with the digital
valve energized before regulation starts. It ranges from 0 to 10 seconds (factory setting =
5 seconds).
2.15 Rescue mode (emergency mode)
In case of controller malfunction, the unit provides an emergency operation mode. The controller will
be completely bypassed and the system will continue to run based on low-pressure switch (
B10
)
cycling. The f unctionality of the high-pressure protection devices (
B21 & B22
) remains active for
saf ety.
NOTE: The low-pressure switch B10 in standard configuration is used as a safety device.
When activating the emergency running mode the cut-in and cut-out setpoints must be
adjusted according to the application requirements.
2.15.1 Functionality
The emergency mode can be activated by means of the "rescue mode" switch
S3
.
There are 2 circuit breakers (S1 [Compressor 1 ENABLE or STOP] and S2 [Compressor 2 ENABLE
or STOP]) to activate the compressors (the digital compressor will perf orm as the f ixed-speed
compressor [= 100 % capacity]). In emergency mode, the system operator must decide if one or two
compressors should be activated to provide sufficient cooling capacity. Switching off one of the two
compressors with S1 or S2 will divides the cooling capacity by half. A time delay can be adjusted
using relay K42 to avoid compressor cycling in rescue mode (f actory setting = 10 minutes). If two
compressors are activated in rescue mode (S11 & S12) both compressors will always run in parallel.
Also, the time delay is always applied to both compressors in parallel.
Compressor control is achieved by low-pressure switch
B10
. In standard operation mode, the
B10
low-pressure cut-out switch is used as a safety device. In rescue operation mode, the settings must
be adapted to installation requirements. The time delay for the compressor starts as soon the cut-in
value of
B10
is reached. After time delay the active compressor (or both) will run with 100 % cooling
capacity until low-pressure cut-out value
B10
is reached then the compressor(s) will stop.
The f ans are automatically activated with the rescue mode switch. The EC f ans are programmed to
run at maximum speed during emergency mode by help of input
D1
on the EC fan.
There is no need f or any adjustments on the fans in this operation mode.
Figure 20: Rescue mode
– Control panel front and bottom views
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